feat(deltachat-repl): add send-sync command

This allows to send send messages when disconnected
using `send_msg_sync` to create a dedicated connection
and send a single message.

The command can be used for measuring
the duration of SMTP connection establishment.

deltachat-repl/src/main.rs

@@ -179,7 +179,7 @@ const DB_COMMANDS: [&str; 11] = [
     "housekeeping",
 ];
 
-const CHAT_COMMANDS: [&str; 38] = [
+const CHAT_COMMANDS: [&str; 39] = [
     "listchats",
     "listarchived",
     "start-realtime",
@@ -199,6 +199,7 @@ const CHAT_COMMANDS: [&str; 38] = [
     "dellocations",
     "getlocations",
     "send",
+    "send-sync",
     "sendempty",
     "sendimage",
     "sendsticker",